EP0588806B1 - Process for manufacturing rod-like preforms - Google Patents

Process for manufacturing rod-like preforms Download PDF

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Publication number
EP0588806B1
EP0588806B1 EP92909441A EP92909441A EP0588806B1 EP 0588806 B1 EP0588806 B1 EP 0588806B1 EP 92909441 A EP92909441 A EP 92909441A EP 92909441 A EP92909441 A EP 92909441A EP 0588806 B1 EP0588806 B1 EP 0588806B1
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EP
European Patent Office
Prior art keywords
starting body
starting
preform
collapsing
zone
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP92909441A
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German (de)
French (fr)
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EP0588806A1 (en
Inventor
Helmut Leber
Hartwig Schaper
Norbert Treber
Gerhart Vilsmeier
Klaus Reimann
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Heraeus Quarzglas GmbH and Co KG
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Heraeus Quarzglas GmbH and Co KG
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/012—Manufacture of preforms for drawing fibres or filaments
    • C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
    • C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
    • C03B37/01861—Means for changing or stabilising the diameter or form of tubes or rods
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B23/00—Re-forming shaped glass
    • C03B23/04—Re-forming tubes or rods
    • C03B23/047—Re-forming tubes or rods by drawing
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/012—Manufacture of preforms for drawing fibres or filaments
    • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
    • C03B37/01225—Means for changing or stabilising the shape, e.g. diameter, of tubes or rods in general, e.g. collapsing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00—Technologies relating to the processing of minerals
    • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
    • Y02P40/57—Improving the yield, e-g- reduction of reject rates

Definitions

  • the invention relates to a method for producing a rod-shaped preform for optical fibers with a core and with at least one sheath enveloping the core and having a lower refractive index than the core, by collapsing a tubular starting body in a collapsing area, the output -Body seen in the radial direction over its wall thickness in at least one interface area has a change in refractive index and wherein during the collapse by continuing evacuation in the tubular part of the output body, an internal pressure reduced compared to the external pressure acting on the output body from the outside is maintained, and the preform is continuously withdrawn from the heating zone.
  • the tubular starting body can be produced by depositing particles on a mandrel which consists, for example, of glass, graphite or aluminum oxide. According to the desired radial refractive index profile of the preform, the deposited particles are either admixed with dopants or z. B. also diffused into the open-pore soot body created by particle separation.
  • the removal of the mandrel causes disturbances in the inner surface of the tubular output body produced.
  • the inner surfaces of the tubular starting bodies are generally treated in different cleaning, smoothing and / or drying processes.
  • the tubular starting body is softened starting from one end, continuously over its length in a heating zone, so that it collapses into a solid body, the preform.
  • a method for producing a preform for drawing optical fibers in which a quartz glass tube, which has a non-linear refractive index curve over its wall thickness in the radial direction due to different germanium doping, is fed vertically to a heating zone and remains connected to a vacuum pump during the collapse in a heating zone, the negative pressure within the glass tube being selected so that there is as little depletion of dopant materials as possible in the center of the preform.
  • the glass fiber is drawn from a tubular glass body which has layers with different refractive indices, the glass tube being closed on both sides and, to facilitate the collapsing process, the glass tube - Inside is evacuated during fiber drawing.
  • the known methods have in common that the entire inner surface of the tubular starting body is mapped onto the center of the preform when it collapses.
  • disturbances in the inner surface of the tubular body for example due to impurities, moisture or other surface defects, lead to inhomogeneities in the center of the preform.
  • they are generally particularly troublesome.
  • oval or jacket-shaped deformations of the core regions of the preform can also frequently be observed.
  • EP-A1-0 458 017 describes to feed a quartz glass tube to an oven while rotating, and to continuously collapse therein into a homogeneous quartz glass rod. In this case, a negative pressure is maintained in the not yet collapsed, tubular part of the quartz glass tube in such a way that a stem is formed from the collapsing quartz glass and is continuously withdrawn against the pulling direction of the quartz glass tube.
  • the present invention has for its object to enable the production of low-interference, rod-shaped preforms for optical elements.
  • the object is achieved in that the starting body is fed continuously with rotation and horizontally to a heating zone, the outer dimensions and inner dimensions of the starting body, the distance of the interface area from the inner surface of the starting body , the viscosity of the material of the starting body in the collapsing area, the pressure difference between the internal pressure and the outside pressure, the level of the internal pressure and the pulling-off speed of the preform and the feeding speed of the starting body are chosen such that from the collapsing area, against the pulling direction of the preform, a stem made of core material is formed in the axis of the starting body.
  • the fact that the geometry of the starting body and the process parameters during collapse are set such that a stem is formed from the collapsing area in the axis of the starting body against the pulling direction of the collapsed preform, premature collapse of opposing inner wall surfaces of the Starting body prevented.
  • the stalk that forms thus stabilizes the symmetry of the softening starting body immediately in front of the collapsing area and facilitates its transfer into the preform.
  • the material of the inner surface layer of the initial body is turned inside out and removed from the collapsing area in the stalk that forms.
  • the center of the collapsed preform which thus does not contain any material that had previously formed a surface, is thereby essentially free of disturbances, including those that may be caused by material evaporation in the heating zone.
  • the non-linear refractive index curve over the wall thickness of the starting body is caused by different concentrations of dopants in the material layers of the starting body.
  • the term interface area is understood to mean the area from which a gradual or continuous change in the refractive index occurs in the radial direction and in which the interface between core and cladding runs in the preform.
  • the viscosity of the material of the starting body also has different values, so that the formation of the stem is facilitated in the collapsing area due to the non-linear viscosity curve seen radially over the wall thickness of the starting body.
  • the starting body is fed to a fixed heating zone or, in a kinematic reversal, the heating zone is led over a stationary starting body.
  • the method according to the invention is particularly suitable for the collapse of hollow cylinders. It has proven useful to rotate the hollow cylinder and the preform around the longitudinal axis at a speed between 5 rpm and 50 rpm during the collapse. The rotation compensates for random asymmetries within the heating zone and stabilizes the stem that forms in the center of the hollow cylinder.
  • An initial body geometry has proven to be advantageous in which the inside diameter is between 10 mm and 120 mm, the ratio of outside to inside diameter being in the range from 1.5 to 3 and the distance of the at least one interface area from the inside surface of the original body is at least 3 percent of its wall thickness.
  • the temperature in the heating zone is preferably set so high that a viscosity of the material in the range of 10 3 dPas to 10 7 dPas is achieved in the collapsing area.
  • Values up to a maximum of 1008 mbar have been found to be suitable for the internal pressure in the tubular part of the starting body, which also determines the speed at which the stem is formed and the mass of material applied to build up the stem, the pressure difference between the internal pressure and the external pressure acting on the starting body with values between 5 mbar and 813 mbar is expediently chosen such that the starting body is not deformed in an uncontrolled manner in the region of the heating zone.
  • the preform In order to achieve an economical mass throughput despite sufficient heating of the material and sufficient thermal stability in the collapsing area, the preform has to be pulled out of the collapsing area between 10 mm / min and 80 mm / min and a feeding speed of the exit Body for the heating zone between 8 mm / min and 35 mm / min.
  • the method according to the invention has proven particularly useful for the collapse of starting bodies in which the viscosity decreases from the inside to the outside at a given temperature.
  • suitable dopant concentrations of the innermost layer of the starting body can be used to set high viscosity differences between this layer and an adjacent, but further outward layer, so that the inner layer in the collapsing area is easily peeled off from the adjacent layer and turned over as a forming stem can.
  • the process is particularly simple when using starting bodies which have a step index course of the refractive index over their wall thickness.
  • the risk of mixing areas of different refractive indices through a possible asymmetrical formation of the stem is thereby largely reduced.
  • the method has become for the collapse of starting bodies which consist predominantly of SiO 2 , in particular those which, in the radial direction, have at least one layer of germanium-doped SiO 2 , and those which, in the radial direction, have at least one layer of undoped SiO 2 and adjacent to it and further out have at least one cladding glass layer made of fluorine-doped SiO 2 , proven to be advantageous.
  • the reference numeral 12 denotes an electrical resistance heater, which envelops the heating zone 1, which encloses a section of a quartz glass tube 2 to be collapsed and an already collapsed preform 3.
  • the inner walls 4 of the quartz glass tube 2 collapse in a collapsing area 5, a stem 6 being formed and being pulled out of the collapsing area 5 counter to the direction in which the preform 3 is pulled off.
  • the direction of removal of the preform 3 is indicated by the directional arrow 7, that of the stem by the directional arrow 8.
  • the quartz glass tube 2 is closed on its end facing away from the collapsing region 5 with a stopper 10.
  • the quartz glass tube 2 which has an outer diameter of 120 mm and an inner diameter of 60 mm, has an innermost layer with a layer thickness of approximately 6 mm, a core glass layer 13 made of pure, synthetic quartz glass and a jacket glass layer adjacent to it and further out 14 made of synthetic quartz glass doped with 0.5% by weight fluorine (for reasons of clarity, the layer thicknesses are not shown to scale in the figure).
  • the quartz glass tube 2 is oriented horizontally and, with a continuous rotation of 20 rpm, is fed to the heating zone 1 at a feed rate of 23 mm / min and heated there to a temperature of around 2100 ° C.
  • the quartz glass In the collapsing area 5, the quartz glass has an average viscosity of 10 5 dPas.
  • the vacuum pump 9 maintains an internal pressure of 900 mbar in the quartz glass tube 2, so that a pressure difference of 113 mbar is maintained compared to the atmospheric pressure applied to the outside of the quartz glass tube surface.
  • the pull-off speed of the preform 3 is 23.5 mm / min and is thus slightly higher than the feed speed of the quartz glass tube 2. As a result, the quartz glass tube 2 and the quartz glass preform 3 are constantly kept in tension.
  • a stem 6 is formed in the axis of the quartz glass tube 2, which stem is composed of material from the areas 11 near the surface (indicated by darker hatching in the figure) of the inner walls 4 of the quartz glass tube 2, which are in the collapsing area 5 have such a low viscosity that they are deformed by the pressure or vacuum forces acting in the longitudinal axis direction against the pulling direction 7 of the preform 3 and turned inside out in the direction of the stem growth 8. With the stem 6, the soiling and disturbances of the areas 11 near the surface are thus removed from the collapsing area 5.
  • the formation of the stem 6 prevents the inner walls 4 of the quartz glass tube 2 from collapsing, thus stabilizing the symmetry of the quartz glass tube 2 directly in front of the collapsing region 5 and transmitting it in the preform 3.
  • the diameter of the preform 3 thus produced is approximately 96 mm. approx. 8 mm of this applies to the core glass area.
  • the stem 6 has a diameter of approximately 40 mm.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Manufacture, Treatment Of Glass Fibers (AREA)

Abstract

A process is known for manufacturing rod-like preforms (3) for optical fibres by collapsing a tubular basic body (14). In order to improve such a process, so that preforms as fault-free as possible can be obtained, a rotating tubular basic body (14) is continuously and horizontally supplied into a heating zone. Outer and inner dimensions of the working body (14), the spacing between the boundary surface zone and the inner surface (13) of the basic body, the viscosity of the basic body (14) material in a collapsing zone, the difference between the inner and outer pressures, the height of the inner pressure, the preform haul-off-speed and the feed speed of the basic body are selected so that a stem (6) made of the core material of the basic body is formed from the collapsing zone in the opposite direction to the preform (3) hauling direction, in the axis of the basic body (14).

Description

Die Erfindung betrifft ein Verfahren zur Herstellung einer stabförmigen Vorform für optische Fasern mit einem Kern und mit mindestens einem, den Kern umhüllenden und eine niedrigere Brechzahl als der Kern aufweisenden Mantel, durch Kollabieren eines rohrförmigen Ausgangs-Körpers in einem Kollabier-Bereich, wobei der Ausgangs-Körper in radialer Richtung gesehen über seine Wandstärke in mindestens einem Grenzflächenbereich eine Brechzahländerung aufweist und wobei während des Kollabierens durch fortgesetztes Evakuieren im rohrförmigen Teil des Ausgangs-Körpers ein gegenüber dem von außen auf den Ausgangs-Körper einwirkenden Außendruck verminderter Innendruck aufrechterhalten, und die Vorform kontinuierlich aus der Erhitzungszone abgezogen wird.The invention relates to a method for producing a rod-shaped preform for optical fibers with a core and with at least one sheath enveloping the core and having a lower refractive index than the core, by collapsing a tubular starting body in a collapsing area, the output -Body seen in the radial direction over its wall thickness in at least one interface area has a change in refractive index and wherein during the collapse by continuing evacuation in the tubular part of the output body, an internal pressure reduced compared to the external pressure acting on the output body from the outside is maintained, and the preform is continuously withdrawn from the heating zone.

Derartige Verfahren zur Herstellung von Vorformen, insbesondere für optische Fasern, sind allgemein bekannt. Die Herstellung des rohrförmigen Ausgangs-Körpers kann durch Abscheiden von Partikeln auf einem Dorn erfolgen, der beispielsweise aus Glas, Graphit oder Aluminiumoxid besteht. Entsprechend dem gewünschten radialen Brechzahlprofil der Vorform werden den abgeschiedenen Partikeln entweder Dotiermittel beigemischt oder z. B. auch in den durch die Partikelabscheidung entstandenen offenporigen "Soot-Körper" eindiffundiert.Such methods for the production of preforms, in particular for optical fibers, are generally known. The tubular starting body can be produced by depositing particles on a mandrel which consists, for example, of glass, graphite or aluminum oxide. According to the desired radial refractive index profile of the preform, the deposited particles are either admixed with dopants or z. B. also diffused into the open-pore soot body created by particle separation.

Die Entfernung des Dornes, beispielsweise durch Herausziehen, Herausbohren oder Herausätzen, verursacht Störungen der Innenoberfläche des erzeugten, rohrförmigen Ausgangs-Körpers. Mit dem Ziel der Verminderung von Oberflächendefekten und Materialinhomogenitäten werden die Innenoberflächen der rohrförmigen Ausgangs-Körpern im allgemeinen in unterschiedlichen Reinigungs-Glättungs- und/oder Trocknungsverfahren nachbehandelt.The removal of the mandrel, for example by pulling out, drilling out or etching out, causes disturbances in the inner surface of the tubular output body produced. With the aim of reducing surface defects and material inhomogeneities, the inner surfaces of the tubular starting bodies are generally treated in different cleaning, smoothing and / or drying processes.

Zum Zweck des Kollabierens wird der rohrförmige Ausgangs-Körper bei den bekannten Verfahren von einem Ende beginnend, fortlaufend über seine Länge in einer Erhitzungszone erweicht, so daß er zu einem Vollkörper, der Vorform, zusammenfällt.In the known methods, for the purpose of collapsing, the tubular starting body is softened starting from one end, continuously over its length in a heating zone, so that it collapses into a solid body, the preform.

Aus der EP-A2-0 163 071 ist ein Verfahren zum Herstellen einer Vorform zum Ziehen von Lichtleiffasern bekannt, bei dem ein Quarzglasrohr, das in radialer Richtung gesehen über seine Wandstärke aufgrund unterschiedlicher Germanium-Dotierung einen nicht linearen Brechzahlverlauf aufweist, vertikal einer Erhitzungszone zugeführt und während des Kollabierens in einer Erhitzungszone mit einer Vakuumpumpe verbunden bleibt, wobei der Unterdruck innerhalb des Glasrohres so gewählt werden soll, daß möglichst keine Verarmung an Dotiermaterialien im Zentrum der Vorform auftritt.From EP-A2-0 163 071 a method for producing a preform for drawing optical fibers is known, in which a quartz glass tube, which has a non-linear refractive index curve over its wall thickness in the radial direction due to different germanium doping, is fed vertically to a heating zone and remains connected to a vacuum pump during the collapse in a heating zone, the negative pressure within the glass tube being selected so that there is as little depletion of dopant materials as possible in the center of the preform.

In einem aus der EP-A1-0 100 174 bekannten Verfahren zur Herstellung einer optischen Glasfaser, wird die Glasfaser aus einem rohrförmigen Glaskörper, der Schichten mit unterschiedlichen Brechungsindizes aufweist, gezogen, wobei das Glasrohr beidseitig verschlossen und, zur Erleichterung des Kollabiervorganges, das Glasrohr-Innere während des Faserziehens evakuiert ist.In a method for producing an optical glass fiber known from EP-A1-0 100 174, the glass fiber is drawn from a tubular glass body which has layers with different refractive indices, the glass tube being closed on both sides and, to facilitate the collapsing process, the glass tube - Inside is evacuated during fiber drawing.

Die bekannten Verfahren haben gemeinsam, daß die gesamte Innenoberfläche des rohrförmigen Ausgangs-Körpers beim Kollabieren auf das Zentrum der Vorform abgebildet wird. Neben Problemen durch Blasenbildung aufgrund von Gaseinschlüssen oder von Dotierstoffverarmung durch Abdampfen von Dotiermaterial während des Kollabiervorganges, führen auch Störungen der Innenoberfläche des rohrförmigen Körpers, etwa aufgrund von Verunreinigungen, Feuchtigkeit oder anderen Oberflächendefekten zu Inhomogenitäten im Zentrum der Vorform. Gerade dort sind sie jedoch im allgemeinen besonders störend. Häufig sind bei den unter Mitwirkung von Unterdruck kollabierten Vorformen auch ovale oder mantelförmige Verformungen der Kernbereiche der Vorform zu beobachten.The known methods have in common that the entire inner surface of the tubular starting body is mapped onto the center of the preform when it collapses. In addition to problems due to bubble formation due to gas inclusions or dopant depletion due to the evaporation of dopant during the collapse process, disturbances in the inner surface of the tubular body, for example due to impurities, moisture or other surface defects, lead to inhomogeneities in the center of the preform. There, however, they are generally particularly troublesome. In the case of the preforms which collapsed with the aid of negative pressure, oval or jacket-shaped deformations of the core regions of the preform can also frequently be observed.

Aus der EP-A1-0 458 017 ist zur Herstellung eines homogenen Quarzglasstabes beschrieben, ein Quarzglasrohr unter Rotation einem Ofen zuzuführen, und darin kontinuierlich zu einem homogenen Quarzglasstab zu kollabieren. Dabei wird ein Unterdruck im noch nicht kollabierten, rohrförmigen Teil des Quarzglasrohres derart aufrechterhalten, daß sich aus dem kollabierenden Quarzglas ein Stengel bildet, der entgegen der Abziehrichtung des Quarzglasrohres kontinuierlich abgezogen wird.For the production of a homogeneous quartz glass rod, EP-A1-0 458 017 describes to feed a quartz glass tube to an oven while rotating, and to continuously collapse therein into a homogeneous quartz glass rod. In this case, a negative pressure is maintained in the not yet collapsed, tubular part of the quartz glass tube in such a way that a stem is formed from the collapsing quartz glass and is continuously withdrawn against the pulling direction of the quartz glass tube.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, die Herstellung störungsarmer, stabförmiger Vorformen für optische Elemente zu ermöglichen.The present invention has for its object to enable the production of low-interference, rod-shaped preforms for optical elements.

Die Aufgabe wird ausgehend von einem Verfahren der eingangs genannten Art erfindungsgemäß dadurch gelöst, daß der Ausgangs-Körper kontinuierlich unter Rotation und horizontal einer Erhitzungszone zugeführt wird, wobei Außenmaße und Innenmaße des Ausgangs-Körpers, der Abstand des Grenzflächenbereichs von der Innenoberfläche des Ausgangs-Körpers, die Viskosität des Materials des Ausgangs-Körpers im Kollabier-Bereich, die Druckdifferenz zwischen dem Innendruck und dem Außendruck, die Höhe des Innendrucks sowie die Abziehgeschwindigkeit der Vorform und die Zuführgeschwindigkeit des Ausgangs-Körpers so gewählt werden, daß aus dem Kollabier-Bereich, entgegen der Abziehrichtung der Vorform, in der Achse des Ausgangs-Körpers, ein aus Kern-Material bestehender Stengel gebildet wird.Based on a method of the type mentioned at the outset, the object is achieved in that the starting body is fed continuously with rotation and horizontally to a heating zone, the outer dimensions and inner dimensions of the starting body, the distance of the interface area from the inner surface of the starting body , the viscosity of the material of the starting body in the collapsing area, the pressure difference between the internal pressure and the outside pressure, the level of the internal pressure and the pulling-off speed of the preform and the feeding speed of the starting body are chosen such that from the collapsing area, against the pulling direction of the preform, a stem made of core material is formed in the axis of the starting body.

Dadurch, daß die Geometrie des Ausgangs-Körpers und die Verfahrensparameter beim Kollabieren so eingestellt werden, daß aus dem Kollabier-Bereich in der Achse des Ausgangs-Körpers ein Stengel entgegen der Abziehrichtung der kollabierten Vorform gebildet wird, wird ein vorzeitiges Zusammenklappen sich gegenüberliegender Innenwandflächen des Ausgangs-Körpers verhindert. Der sich bildende Stengel stabilisiert somit unmittelbar vor dem Kollabier-Bereich die Symmetrie des erweichenden Ausgangs-Körpers und erleichtert deren Übertragung in die Vorform. Gleichzeitig wird das Material der Innen-Oberflächenschicht des Ausgangs-Körpers umgestülpt und im sich bildenden Stengel aus dem Kollabier-Bereich entfernt. Das Zentrum der kollabierten Vorform, das somit kein Material enthält, das vorher einmal eine Oberfläche gebildet hatte, ist dadurch im wesentlichen frei von Störungen, auch solchen, die aufgrund von Materialabdampfungen in der Erhitzungszone verursacht sein können, herstellbar. Der nicht lineare Brechzahlverlauf über die Wandstärke des Ausgangs-Körpers wird aufgrund von unterschiedlichen Konzentrationen von Dotierstoffen in den Materialschichten des Ausgangs-Körpers hervorgerufen. Unter dem Begriff Grenzflächenbereich wird dabei der Bereich verstanden, von dem aus in radialer Richtung gesehen eine stufenweise oder eine stetige Änderung der Brechzahl auftritt und in dem in der Vorform die Grenzfläche zwischen Kern und Mantel verläuft. Je nach Dotierstoffkonzentrationen weist auch die Viskosität des Materials des Ausgangs-Körpers unterschiedliche Werte auf, so daß im Kollabier-Bereich aufgrund des radial über die Wandstärke des Ausgangs-Körpers gesehen, nicht linearen Viskositätsverlaufes, die Bildung des Stengels erleichtert wird.The fact that the geometry of the starting body and the process parameters during collapse are set such that a stem is formed from the collapsing area in the axis of the starting body against the pulling direction of the collapsed preform, premature collapse of opposing inner wall surfaces of the Starting body prevented. The stalk that forms thus stabilizes the symmetry of the softening starting body immediately in front of the collapsing area and facilitates its transfer into the preform. At the same time, the material of the inner surface layer of the initial body is turned inside out and removed from the collapsing area in the stalk that forms. The center of the collapsed preform, which thus does not contain any material that had previously formed a surface, is thereby essentially free of disturbances, including those that may be caused by material evaporation in the heating zone. The non-linear refractive index curve over the wall thickness of the starting body is caused by different concentrations of dopants in the material layers of the starting body. The term interface area is understood to mean the area from which a gradual or continuous change in the refractive index occurs in the radial direction and in which the interface between core and cladding runs in the preform. Depending on the dopant concentrations, the viscosity of the material of the starting body also has different values, so that the formation of the stem is facilitated in the collapsing area due to the non-linear viscosity curve seen radially over the wall thickness of the starting body.

Zur Erzielung dieser Vorteile ist es gleichgültig, ob der Ausgangs-Körper einer ortsfesten Erhitzungszone zugeführt oder in kinematischer Umkehr die Erhitzungszone über einen ortsfesten Ausgangs-Körper hinweggeführt wird.In order to achieve these advantages, it does not matter whether the starting body is fed to a fixed heating zone or, in a kinematic reversal, the heating zone is led over a stationary starting body.

Besonders geeignet ist das erfindungsgemäße Verfahren für das Kollabieren von Hohlzylindern. Dabei hat es sich bewährt, den Hohlzylinder und die Vorform während des Kollabierens mit einer Geschwindigkeit zwischen 5 U/min und 50 U/min um die Längsachse zu rotieren. Durch die Rotation werden zufällige Asymetrien innerhalb der Erhitzungszone ausgeglichen und der sich bildende Stengel im Zentrum des Hohlzylinders stabilisiert. Dabei hat sich eine Ausgangs-Körper-Geometrie als vorteilhaft erwiesen, bei der der Innendurchmesser zwischen 10 mm und 120 mm wobei das Verhältnis von Außen- zu Innendurchmesser im Bereich von 1,5 bis 3 liegt und der Abstand des mindestens einen Grenzflächenbereiches von der Innenoberfläche des Ausgangs-Körpers mindestens 3 Prozent von dessen Wandstärke beträgt. Da der Kollabiervorgang möglichst schnell ablaufen sollte, wird die Temperatur in der Erhitzungszone vorzugsweise so hoch eingestelt, daß im Kollabier-Bereich eine Viskosität des Werkstoffes im Bereich von 103 dPas bis 107 dPas erzielt wird. Für den Innendruck im rohrförmigen Teil des Ausgangs-Körpers, der mitbestimmend für die Geschwindigkeit, mit der der Stengel gebildet wird und für die für den Aufbau des Stengels aufgebrachte Werkstoffmasse ist, haben sich Werte bis maximal 1008 mbar als geeignet erwiesen, wobei die Druckdifferenz zwischen dem Innendruck und dem auf den Ausgangs-Körper wirkenden Außendruck mit Werten zwischen 5 mbar und 813 mbar zweckmäßig so gewählt wird, daß der Ausgangs-Körper im Bereich der Erhitzungszone nicht unkontrolliert verformt wird. Um trotz einer genügenden Durchheizung des Werkstoffes und einer ausreichenden thermischen Stabilität im Kollabier-Bereich, dennoch einen wirtschaftlichen Massendurchsatz zu erreichen, hat sich eine Abziehgeschwindigkeit der Vorform aus dem Kollabier-Bereich zwischen 10 mm/min und 80 mm/min und eine Zuführgeschwindigkeit des Ausgangs-Körpers zur Erhitzungszone zwischen 8 mm/min und 35 mm/min bewährt.The method according to the invention is particularly suitable for the collapse of hollow cylinders. It has proven useful to rotate the hollow cylinder and the preform around the longitudinal axis at a speed between 5 rpm and 50 rpm during the collapse. The rotation compensates for random asymmetries within the heating zone and stabilizes the stem that forms in the center of the hollow cylinder. An initial body geometry has proven to be advantageous in which the inside diameter is between 10 mm and 120 mm, the ratio of outside to inside diameter being in the range from 1.5 to 3 and the distance of the at least one interface area from the inside surface of the original body is at least 3 percent of its wall thickness. Since the collapsing process should take place as quickly as possible, the temperature in the heating zone is preferably set so high that a viscosity of the material in the range of 10 3 dPas to 10 7 dPas is achieved in the collapsing area. Values up to a maximum of 1008 mbar have been found to be suitable for the internal pressure in the tubular part of the starting body, which also determines the speed at which the stem is formed and the mass of material applied to build up the stem, the pressure difference between the internal pressure and the external pressure acting on the starting body with values between 5 mbar and 813 mbar is expediently chosen such that the starting body is not deformed in an uncontrolled manner in the region of the heating zone. In order to achieve an economical mass throughput despite sufficient heating of the material and sufficient thermal stability in the collapsing area, the preform has to be pulled out of the collapsing area between 10 mm / min and 80 mm / min and a feeding speed of the exit Body for the heating zone between 8 mm / min and 35 mm / min.

Es hat sich als vorteilhaft erwiesen, die Vorform und den Ausgangs-Körper mit derselben Geschwindigkeit und in gleicher Umdrehungsrichtung zu rotieren. Vermischungen von Schichten des Ausgangs-Körpers und der Vorform mit unterschiedlichen Brechzahlen werden dadurch vermieden.It has proven to be advantageous to rotate the preform and the starting body at the same speed and in the same direction of rotation. Mixing layers of the starting body and the preform with different refractive indices is avoided.

Besonders bewährt hat sich das erfindungsgemäße Verfahren für das Kollabieren von Ausgangs-Körpern, bei denen sich die Viskosität bei gegebener Temperatur von innen nach außen verringert. So lassen sich beispielsweise durch geeignete Dotierstoffkonzentrationen der innersten Schicht des Ausgangs-Körpers hohe Viskositätsunterschiede zwischen dieser Schicht und einer benachbarten, aber weiter außen liegenden Schicht einstellen, so daß die innere Schicht im Kollabierbereich leicht von der benachbarten Schicht abgeschält und als sich bildender Stengel umgestülpt werden kann.The method according to the invention has proven particularly useful for the collapse of starting bodies in which the viscosity decreases from the inside to the outside at a given temperature. For example, suitable dopant concentrations of the innermost layer of the starting body can be used to set high viscosity differences between this layer and an adjacent, but further outward layer, so that the inner layer in the collapsing area is easily peeled off from the adjacent layer and turned over as a forming stem can.

Besonders einfach gestaltet sich das Verfahren bei der Verwendung von Ausgangs-Körpern, die einen Stufenindex-Verlauf der Brechzahl über ihre Wandstärke aufweisen. Die Gefahr einer Vermischung von Bereichen unterschiedlicher Brechzahlen durch eine eventuelle unsymmetrische Bildung des Stengels wird dadurch weitgehend vermindert. Das Verfahren hat sich zum Kollabieren von Ausgangs-Körpern, die überwiegend aus SiO2 bestehen, insbesondere solchen, die in radialer Richtung gesehen mindestens eine Schicht aus Germanium-dotiertem SiO2 aufweisen, sowie solchen, die in radialer Richtung gesehen mindestens eine Schicht aus undotiertem SiO2 und dazu benachbart und weiter außen liegend mindestens eine Mantelglas-Schicht aus Fluor-dotiertem SiO2 aufweisen, als vorteilhaft erwiesen.The process is particularly simple when using starting bodies which have a step index course of the refractive index over their wall thickness. The risk of mixing areas of different refractive indices through a possible asymmetrical formation of the stem is thereby largely reduced. The method has become for the collapse of starting bodies which consist predominantly of SiO 2 , in particular those which, in the radial direction, have at least one layer of germanium-doped SiO 2 , and those which, in the radial direction, have at least one layer of undoped SiO 2 and adjacent to it and further out have at least one cladding glass layer made of fluorine-doped SiO 2 , proven to be advantageous.

Das erfindungsgemäße Verfahren wird anhand einer schematischen Darstellung nachfolgend beispielhaft beschrieben.The method according to the invention is described below by way of example using a schematic illustration.

Mit der Bezugsziffer 12 ist eine elektrische Widerstandsheizung bezeichnet, die die Erhitzungszone 1 umhüllt, die einen Abschnitt eines zu kollabierenden Quarzglasrohres 2 und einer bereits kollabierten Vorform 3 umschließt. Innerhalb der Erhitzungszone 1 fallen die Innenwandungen 4 des Quarzglasrohres 2 in einem Kollabier-Bereich 5 zusammen, wobei ein Stengel 6 gebildet und entgegen der Abziehrichtung der Vorform 3 aus dem Kollabier-Bereich 5 abgezogen wird. Die Abziehrichtung der Vorform 3 ist mit dem Richtungspfeil 7, die des Stengels mit dem Richtungspfeil 8 gekennzeichnet. Das Quarzglasrohr 2 ist an seiner, dem Kollabier-Bereich 5 abgewandten Stirnseite mit einem Stopfen 10 verschlossen. Innerhalb des Quarzglasrohres 2 wird während des Kollabierens ein Innendruck von 900 mbar mittels einer Vakuumpumpe 9 gehalten, die über eine vakuumdichte Durchführung durch den Stopfen 10 an das Quarzglasrohr 2 angeschlossen ist. Das Quarzglasrohr 2, das einen Außendurchmesser von 120 mm und einen Innendurchmesser von 60 mm hat, weist als innerste Schicht mit einer Schichtdicke von etwa 6 mm eine Kernglas-Schicht 13 aus reinem, synthetischem Quarzglas und dazu benachbart und weiter außen liegend eine Mantelglas-Schicht 14 aus mit 0,5 Gew.-% Fluor dotiertem, synthetischem Quarzglas auf (der Deutlichkeit wegen sind die Schichtdicken in der Figur nicht maßstabsgerecht dargestellt). Das Quarzglasrohr 2 wird horizontal orientiert und unter kontinuierlicher Rotation von 20 U/min mit einer Zuführgeschwindigkeit von 23 mm/min der Erhitzungszone 1 zugeführt und dort auf eine Temperatur um 2100°C aufgeheizt. Im Kollabier-Bereich 5 hat das Quarzglas dabei eine mittlere Viskosität von 105 dPas. Während des Kollabierens hält die Vakuumpumpe 9 im Quarzglasrohr 2 einen Innendruck von 900 mbar aufrecht, so daß gegenüber dem außen an der Quarzglasrohr-Oberfläche anliegenden Atmosphärendruck eine Druckdifferenz von 113 mbar erhalten bleibt. Die Abziehgeschwindigkeit der Vorform 3 beträgt 23,5 mm/min und ist damit geringfügig höher als die Zuführgeschwindigkeit des Quarzglasrohres 2. Dadurch werden das Quarzglasrohr 2 und die Quarzglas-Vorform 3 ständig auf Zug gehalten.The reference numeral 12 denotes an electrical resistance heater, which envelops the heating zone 1, which encloses a section of a quartz glass tube 2 to be collapsed and an already collapsed preform 3. Inside the heating zone 1, the inner walls 4 of the quartz glass tube 2 collapse in a collapsing area 5, a stem 6 being formed and being pulled out of the collapsing area 5 counter to the direction in which the preform 3 is pulled off. The direction of removal of the preform 3 is indicated by the directional arrow 7, that of the stem by the directional arrow 8. The quartz glass tube 2 is closed on its end facing away from the collapsing region 5 with a stopper 10. An internal pressure of 900 mbar is maintained within the quartz glass tube 2 during the collapse by means of a vacuum pump 9, which is passed through a plug 10 to the quartz glass tube 2 through a vacuum connected. The quartz glass tube 2, which has an outer diameter of 120 mm and an inner diameter of 60 mm, has an innermost layer with a layer thickness of approximately 6 mm, a core glass layer 13 made of pure, synthetic quartz glass and a jacket glass layer adjacent to it and further out 14 made of synthetic quartz glass doped with 0.5% by weight fluorine (for reasons of clarity, the layer thicknesses are not shown to scale in the figure). The quartz glass tube 2 is oriented horizontally and, with a continuous rotation of 20 rpm, is fed to the heating zone 1 at a feed rate of 23 mm / min and heated there to a temperature of around 2100 ° C. In the collapsing area 5, the quartz glass has an average viscosity of 10 5 dPas. During the collapse, the vacuum pump 9 maintains an internal pressure of 900 mbar in the quartz glass tube 2, so that a pressure difference of 113 mbar is maintained compared to the atmospheric pressure applied to the outside of the quartz glass tube surface. The pull-off speed of the preform 3 is 23.5 mm / min and is thus slightly higher than the feed speed of the quartz glass tube 2. As a result, the quartz glass tube 2 and the quartz glass preform 3 are constantly kept in tension.

Aufgrund der oben angeführten Versuchsparameter bildet sich in der Achse des Quarzglasrohres 2 ein Stengel 6 aus, der sich aus Material aus den oberflächennahen Bereichen 11 (in der Figur mit dunklerer Schraffur angedeutet) der Innenwandungen 4 des Quarzglasrohres 2 zusammensetzt, die im Kollabier-Bereich 5 eine so niedrige Viskosität haben, daß sie von den in Längsachsenrichtung, entgegen der Abziehrichtung 7 der Vorform 3 wirkenden Druck- bzw. Vakuumkräften verformt und in Richtung des Stengelwachstums 8 umgestülpt werden. Mit dem Stengel 6 werden somit die Verschmutzungen und Störungen der oberflächennahen Bereiche 11 aus dem Kollabier-Bereich 5 entfernt. Außerdem wird durch die Ausbildung des Stengels 6 ein Zusammenfallen gegenüberliegender Innenwandungen 4 des Quarzglasrohres 2 verhindert und damit die Symmetrie des Quarzglasrohres 2 unmittelbar vor dem Kollabier-Bereich 5 stabilisiert und in der Vorform 3 übertragen. Der Durchmesser des so hergestellten Vorform 3 beträgt ca. 96 mm. davon entfallen auf den Kernglas-Bereich ca. 8 mm. Der Stengel 6 weist einen Durchmesser von etwa 40 mm auf.On the basis of the above-mentioned test parameters, a stem 6 is formed in the axis of the quartz glass tube 2, which stem is composed of material from the areas 11 near the surface (indicated by darker hatching in the figure) of the inner walls 4 of the quartz glass tube 2, which are in the collapsing area 5 have such a low viscosity that they are deformed by the pressure or vacuum forces acting in the longitudinal axis direction against the pulling direction 7 of the preform 3 and turned inside out in the direction of the stem growth 8. With the stem 6, the soiling and disturbances of the areas 11 near the surface are thus removed from the collapsing area 5. In addition, the formation of the stem 6 prevents the inner walls 4 of the quartz glass tube 2 from collapsing, thus stabilizing the symmetry of the quartz glass tube 2 directly in front of the collapsing region 5 and transmitting it in the preform 3. The diameter of the preform 3 thus produced is approximately 96 mm. approx. 8 mm of this applies to the core glass area. The stem 6 has a diameter of approximately 40 mm.

Claims (7)

  1. Process for manufacturing a rod-like preform for optical fibres, having a core and having at least one shell which surrounds the core and has a lower refractive index than the core, by collapsing a tubular starting body (2) in a collapsing zone (5), the starting body (2) exhibiting a change in refractive index in the radial direction over its wall thickness in at least one interfacial zone, and an internal pressure which is lower than the external pressure acting from the outside on the starting body (2) being maintained during the collapsing procedure by continuous evacuation in the tubular part of the starting body (2), and the preform (3) is drawn off continuously from the heating zone (12), characterized in that the starting body (2) is fed continuously, horizontally and with rotation, to a heating zone (12), external dimensions and internal dimensions of the starting body, the distance between the interfacial zone and the inner surface (4) of the starting body (2), the viscosity of the material of the starting body (2) in the collapsing zone (5), the difference between the internal pressure and the external pressure, the magnitude of the internal pressure and the draw-off speed of the preform (3) and the feed speed of the starting body (2) being chosen so that a stem (6) consisting of core material is formed from the collapsing zone (5), in a direction opposite to the draw-off direction (7) of the preform (3), in the axis of the starting body (2).
  2. Process according to Claim 1, characterized in that the starting body (2) and the preform (3) are rotated at a speed in the range from 5 rpm to 50 rpm around the longitudinal axis, that cylindrical starting bodies (2) are formed having an internal diameter in the range from 10 mm to 120 mm, the ratio of external to internal diameter being in the range from 1.5 to 3 and the distance between the one or more interfacial zones and the inner surface of the starting body (2) being at least 3 percent of the wall thickness of the starting body (2), that the viscosity of the material of the starting body (2) in the collapsing zone (5) is adjusted to a value in the range from 103 dPas to 107 dPas, that the internal pressure in the tubular part of the starting body (2) is kept at a value of not more than 1008 mbar and the pressure difference is adjusted to a value in the range from 5 mbar to 813 mbar, and that the draw-off speed of the preform (3) is adjusted to a value in the range between 10 mm/min and 80 mm/min and the feed speed of the starting body (2) is adjusted to a value in the range between 8 mm/min and 35 mm/min.
  3. Process according to Claim 1 or Claim 2, characterized in that the starting body (2) and preform (3) are rotated at the same speed and in the same direction of rotation.
  4. Process according to one or more of Claims 1 to 3, characterized in that starting bodies (2) are used in which the viscosity at a given temperature decreases from the inside to the outside.
  5. Process according to any of Claims 1 to 4, characterized in that starting bodies (2) which essentially comprise SiO2 are used.
  6. Process according to any of Claims 1 to 5, characterized in that starting bodies (2) which have at least one layer of germanium-doped SiO2 are used.
  7. Process according to one or more of Claims 1 to 6, characterized in that starting bodies which, viewed in the radial direction, have at least one layer (14) of undoped SiO2 or of germanium-doped SiO2 (14) and at least one jacket glass layer (15) located further outside and comprising fluorine-doped SiO2 are used.
EP92909441A 1991-05-31 1992-04-30 Process for manufacturing rod-like preforms Expired - Lifetime EP0588806B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE4117817 1991-05-31
DE4117817A DE4117817C2 (en) 1991-05-31 1991-05-31 Process for producing a rod-shaped preform for optical fibers
PCT/EP1992/000939 WO1992021627A1 (en) 1991-05-31 1992-04-30 Process for manufacturing rod-like preforms

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EP0588806A1 EP0588806A1 (en) 1994-03-30
EP0588806B1 true EP0588806B1 (en) 1996-08-07

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CA (1) CA2100070A1 (en)
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DE19958276C1 (en) * 1999-12-03 2001-05-03 Heraeus Quarzglas Quartz glass preform production comprises preparing a quartz glass hollow cylinder collapsed on a quartz glass rod containing a dopant and collapsing the cylinder
JP5093956B2 (en) * 2000-06-09 2012-12-12 ヘレウス・テネボ・ゲゼルシャフト・ミット・ベシュレンクテル・ハフツング Manufacturing method of quartz glass solid cylinder
DE10117153C1 (en) * 2001-04-05 2002-06-13 Heraeus Quarzglas Production of quartz glass cylinders comprises temporarily holding open the lower end of the cylinder during the attracting phase, and producing a gas window in the region of the open lower end whilst a gas stream is fed into the inner bore
NL1019675C2 (en) * 2001-12-28 2003-07-01 Draka Fibre Technology Bv Method for heating a hollow substrate tube into a rod-shaped preform with heating.
DE102008063680A1 (en) 2008-10-10 2010-04-15 Abb Ag Method for teaching (teaching) an industrial robot and a correspondingly equipped industrial robot
DE102015100333A1 (en) * 2015-01-12 2016-07-14 ideas beyond AG Multi-layer paper

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JPS51146243A (en) * 1975-06-11 1976-12-15 Hitachi Ltd Process for manufacturing optical fiber
FR2436111A1 (en) * 1975-10-30 1980-04-11 Haussonne Francois Collapsing of glass tube to make solid rod - where tube is rotated and heated without tension, esp. to mfr. blank for drawing optical waveguide fibres
CA1090134A (en) * 1976-03-22 1980-11-25 Western Electric Company, Incorporated Fabrication of optical fibers with improved cross sectional circularity
DE3206176A1 (en) * 1982-02-20 1983-08-25 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Process for the production of a preform from which optical fibres can be drawn
DE4016030A1 (en) * 1990-05-18 1991-11-21 Heraeus Quarzglas METHOD FOR FORMING A HOLLOW BODY TOOL-FREE

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DE4117817A1 (en) 1992-12-03
CA2100070A1 (en) 1992-12-01
JPH06507370A (en) 1994-08-25
WO1992021627A1 (en) 1992-12-10
JP3207855B2 (en) 2001-09-10
DE4117817C2 (en) 1994-02-03
DE59206873D1 (en) 1996-09-12

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